Appending an object brings duplicated objects
To summarize the answers in the comments, it looks like you can solve the problem by simply deleting the erroneously copied brick(s).

To avoid this problem entirely in the future, you can used an Array modifier on the bricks, then separate them into individually manipulatable meshes using the techniques outlined at How can I use an array modifier to create individually manipulatable objects?.

A third option, depending on the kind of manipulation you are doing to the brick meshes, would be to automate the randomness of the bricks using a Displace modifier (applied after applying an Array modifier). In order to make each one of the bricks have a different deformation, set the Displace modifier setting 'Texture Coordinates' to object and select any object in your scene (though preferably an empty).